The use of halogenated hydrocarbons is widespread and chronic exposure of many individuals is common. Toxicity is associated with the formation of highly reactive free radical intermediates implicated to be involved in the necrosis which occurs in the tissue producing the reactive intermediates. We have shown that CC14, halothane, trichloroethylene, 1,1,1-trichloroethane, CHBr3, CHC13 and Freon 11, CFC13, are metabolized to free radical products in vivo, which can be trapped and analyzed using electron spin resonance techniques. Investigations now in progress will be extended to determine if free radical formation observed during the metabolism of commercially used halogenated hydrocarbons in the liver is correlated with the extent of liver injury as assessed by electron microscopy techniques and serum sorbitol dehydrogenase assays. The compounds to be studied include trichloroethylene, 1,1,1- trichloroethane, 1,1,2-trichloroethane, vinylidene chloride (1,1- dichloroethylene), and trichlorofluoromethane (Freon-11). Using a new spin-trapping agent, 2,4,6-trimethoxyphenyl-t- butylnitrone, both 13CC13 and lipid radicals L have been trapped during the metabolism of 13CC14 in vivo and in vitro. This new spin trapping agent shows promise for investigating the metabolism of halocarbons to free radical products and tissue radical intermediates in organs damaged by these compounds. The advantages of using 13C-labeled compounds to identify carbon-centered radical intermediates in biological systems was demonstrated in this laboratory. A similar strategy will be used in determining the nature of the radicals produced during 13C- labeled trichloroethylene metabolism. It is essential to validate that the free radical phenomena associated with cell membrane damage during in vitro metabolism of a substance also occurs in vivo during exposure of the animal to that substance. It is necessary to determine 1) the extent to which various types of halogenated hydrocarbons form free radicals when metabolized by the mixed function oxidase system; 2) if any of the biological effects of exposure to these compounds can be related to free radical events occurring in vivo; 3) the relationship of radical generation to liver damage; and 4) if the free radical formation and liver injury can be minimized once exposure has occurred. Investigations on the determination of the capacity of free radical quenching and trapping agents for preventing such reactions may indicate both the nature of the toxicity and a practical means for preventing such toxicity.